Chevrolet 70 1969 Series, Руководство по ремонту

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CHASSIS ELECTRICAL AND INSTRUMENTS 12-5
connections at horn relay. Terminal numbers
appearing: on wiring diagrams are stamped on
bottom of the relay base.
Horn button in center of steering wheel is con­
nected in series with the relay operating coil at re­
lay terminal No. 2. When circuit through relay
operating coil is completed at the horn button, a
small amount of current flows from the battery
through the coil winding. With winding energized,
armature is attracted to core and points close.
ALARM
LOW V A C U U M ALARM SYSTEM
The low vacuum alarm system, on vehicles so
equipped, consists of a low vacuum switch, a buzzer,
and a gauge to audibly and visually warn the driver
when vacuum in the system is below a safe limit.
The low vacuum alarm buzzer is mounted on
left side of dash panel inside the cab. When circuit
through buzzer is completed at low vacuum switch,
action of the vibrating armature striking the core
produces a buzzing sound.
Low vacuum alarm system wiring connec­
tions are shown on applicable wiring diagrams.
The alarm buzzer and switch are not repairable
units. If unit becomes inoperative, replace.
LOW AIR PRESSURE ALARM SYSTEM
The low air pressure alarm system, on ve­
hicles so equipped, consists of a low air pressure
switch, a buzzer, and a tell-tale and/or gauge to
audibly and visually warn the driver when air pres­
sure in the system is below a safe limit for brake
operation. Refer to "A IR B R A K E S " (SEC. 5B) for
information on low air pressure switch.
The low air pressure alarm buzzer is mounted
on left side of dash panel inside the cab on con­
ventional cab models; or on instrument panel to
steering column support bracket on tilt cab models.
When circuit through buzzer is completed at low
air pressure switch, action of the vibrating arm ­
ature striking the core produces a buzzing sound.
INSTRUMENTS
CON VENTIO NAL CAB MODELS
A typical instrument cluster used on Series
70 vehicles is shown in figure 7 and a typical
instrument cluster used on Series 80 vehicles
is shown in figure 8. The cluster contains in­
strument lights, tell-tale lights, gauges, speed­
ometer, and tachometer.
Current from the battery (No. 1 terminal) then
flows directly through relay contacts and out No.
3 terminal to the horn. The relay thus provides a
higher voltage to the horn by avoiding voltage drop
through the long circuit through the horn button.
Relay cover can be removed and contact
points can be cleaned. To remove cover, bend
tabs securing cover to relay base. Relay is non-
adjustable, therefore if it becomes inoperative,
replace.
SYSTEM
Low air pressure alarm system wiring con­
nections are shown on applicable wiring diagrams.
In the event of failure, the buzzer must be replaced.
N O T E : This system is part of the "Engine
Alarm System” when vehicle is so equipped.
ENGINE ALARM SYSTEM
This system, used as optional equipment on
some vehicles, audibly and visually warns the
driver of low air pressure, low oil pressure, or
an overheated engine. The alarm system consists
of a low air pressure switch, low oil pressure
switch, hot engine switch, alarm buzzer and rec­
tifier assembly, and a separate tell-tale light for
each condition. The buzzer and rectifier is mounted
on left side of dash panel inside the cab on conven­
tional cab models and on tilt cab models, it is
mounted on instrument panel to steering column
support bracket. Wiring connections are shown on
applicable wiring diagrams.
Buzzer and rectifier assembly consists of a
vibrating armature type relay which produces a
buzzing sound when the circuit through relay coil
is completed by either of three controlling switches
and a three circuit rectifier. The rectifier permits
current flow in one direction only, preventing a
back flow of current from one alarm circuit from
illuminating the other tell-tale lights. Thus, when
only one abnormal condition exists, the buzzer will
sound but only the tell-tale light connected to that
circuit will illuminate.
If alarm buzzer or rectifier assembly does
not operate properly, replace the complete unit.
A N D GAUGES
N O T E : The instruments, gauges, and tell-tale
lights will vary with different truck models, de­
pending upon the size of vehicle and equipment used.
R E M O V A L
I M P O R T A N T : Disconnect negative battery
cable before removing the instrument cluster to
prevent accidental grounding at ammeter.
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L